A styrene polymer produced by the radical polymerization method, etc. has an atactic configuration in stereostructure. It is molded into various shapes by various molding methods such as injection molding, extrusion molding, blow molding, vacuum molding and cast molding, and is widely used for domestic electric appliances, office equipments, domestic appliances, packaging containers, toys, furniture, synthetic papers and other industrial materials.
However, the styrene polymer having an atactic configuration has drawbacks of insufficient heat resistance and chemical resistances.
The group of the present inventors have succeeded to develop a styrene polymer having a high degree of syndiotacticity, and also developed a styrene polymer in which other components are copolymerized with the styrene monomer (Japanese Patent Application Laid-Open Nos. 104818/1987 and 241009/1989). Such polymer or copolymer having a syndiotactic configuration has excellent heat resistance, chemical resistance and electric characteristic, and expected to be applied in various fields.
However, in the above polymer, particularly, syndiotactic polystyrene, glass transition temperature is high, i.e., 90.degree. to 100.degree. C., and melting point is 270.degree. C. Accordingly, the polymer has defects that it cannot sufficiently show its characteristics unless injection molding temperature is set at high temperature. In addition, the molded product obtained by using a high temperature mold is required to be improved in impact resistance. The above polymer has disadvantages in that it has poor compatibility with polyolefins such as polyethylene, polypropylene and the like. Such polymer has insufficient compatibility and adhesion with other resin, inorganic fillers or the like.
Particularly, compared with olefin polymer which is characterized in its flexibility, the syndiotactic polystyrene should be improved in its solvent resistance, heat resistance and impact resistance.
Accordingly, the present inventors have studied intensively to decrease the glass transition temperature of syndiotactic polystyrene to enable injection molding at low temperature and further to improve impact resistance and compatibility and adhesion with other resins including polyolefin and inorganic fillers.
As the results, it has been found that copolymerization of styrene monomer and olefin monomer or diene monomer in the presence of a specific catalyst provides a copolymer having styrene repeating unit chain with syndiotactic configuration copolymerized with olefin component or diene component. Such copolymer has excellent heat resistance and chemical resistance. Further, it can be injection molded at low temperature because of its reduced glass transition temperature. Moreover, it has good compatibility with other resins. Thus it has been found that the objective modification can be attained.. The present invention has been established based on such findings.